The use of POAs and HPAs for the catalytic air oxidation of alkanes such as butane is known. [See, for example, M. Ai, Partial Oxidation of n-Butane with Heteropoly Compound-based Catalysts, Proceedings of the 18th International Congress on Catalysis, Berlin, 1984, Verlag Chemie Vol. 5, page 475]. In addition our patent U.S. Pat. No. 4,803,187 describes the use of HPAs and POAs in liquid phase oxidation of alkanes; this patent is incorporated herein by reference.
HPAs and POAs, both in general, and those which can be used to prepare the catalysts used in our invention, and their preparation are thoroughly described in Heteropoly and Isopoly Oxo-metalates, Pope et al, Springer-Verlag, New York 1983. In order to clarify the terminology used in the art, consider first a specific precursor used in our invention, H.sub.3 PW.sub.12 O.sub.40. Since the cations in this material are hydrogen, the compound is a heteropolyacid. If the cations are not hydrogen but are metals such as an alkali metal, potassium, sodium, or lithium, or are ammonium, as in K.sub.3 PW.sub.12 O.sub.40 or (NH.sub.4).sub.3 PW.sub.12 O.sub.40, then it is obviously no longer an acid, and is referred to as a polyoxoanion.
As described in Pope, HPAs and POAs are cage-like structures with a primary, generally centrally located atom(s) surrounded by the cage framework which contains a plurality of other metal atoms, the same or different, bonded to oxygen atoms. Since the central atom is different from the other metal atoms, it is described as "hetero." The other metal atoms are transition metals and have oxygen bonding such as ##STR1## where four of the singly bonded oxygen atoms are bonded to other M atoms in the framework and the fifth is bonded to the central hetero atom.